Windows 2000 DNS servers support aging and scavenging features. These features
are provided as a mechanism for performing cleanup and removal of stale resource
records (RRs), which can accumulate in zone data over time.

With dynamic update, RRs are automatically added to zones when computers start
on the network. However, in some cases, they are not automatically removed when
computers leave the network. For example, if a computer registers its own host
(A) RR at startup and is later improperly disconnected from the network, its
host (A) RR might not be deleted. If your network has mobile users and computers,
this situation can occur frequently.

If left unmanaged, the presence of stale RRs in zone data might cause some
problems. The following are examples:

If a large number of stale RRs remain in server zones, they can eventually
take up server disk space and cause unnecessarily long zone transfers.

The accumulation of stale RRs at the DNS server can degrade its performance
and responsiveness.

In some cases, the presence of a stale RR in a zone could prevent a DNS
domain name from being used by another computer or host device.

To solve these problems, the DNS Server service has the following features:

Time stamping, based on the current date and time set at the server computer,
for any RRs added dynamically to primary-type zones. In addition, time stamps
are recorded in standard primary zones where aging/scavenging is enabled.

For RRs that you add manually, a time stamp value of zero is used, indicating
that they are not affected by the aging process and can remain without limitation
in zone data unless you otherwise change their time stamp or delete them.

Aging of RRs in local data, based on a specified refresh time period,
for any eligible zones.

Only primary type zones that are loaded by the DNS Server service are eligible
to participate in this process.

Scavenging for any RRs that persist beyond the specified refresh period.

When a Windows 2000 DNS server performs a scavenging operation, it can determine
that RRs have aged to the point of becoming stale and remove them from zone
data. Servers can be configured to perform recurring scavenging operations
automatically, or you can initiate an immediate scavenging operation at
the server.

Caution

By default, the aging and scavenging mechanism is disabled at Windows 2000
DNS servers. It should be enabled only when all parameters are fully understood.
Otherwise, the server could be accidentally configured to delete records
that should not be deleted. If a record is accidentally deleted, not only
will users fail to resolve queries for that record, but any user can create
the record and take ownership of it, even on zones configured for secure
dynamic update.

The server uses the contents of each RR-specific time stamp, along with other
aging/scavenging properties that you can adjust or configure, to determine when
it scavenges records.

Prerequisites for Aging/Scavenging

Before the aging and scavenging features of Windows 2000 DNS can be used, several
conditions must be met:

Scavenging and aging must be enabled both at the DNS server and on the
zone.

By default, aging and scavenging of resource records is disabled.

Resource records must either be dynamically added to zones or manually
modified for use in aging and scavenging operations.

Typically, only those resource records added dynamically using the DNS dynamic
update protocol are subject to aging and scavenging.

You can, however, enable scavenging for other resource records added through
non-dynamic means. For records added to zones in this way, either by loading
a text-based zone file from another DNS server or by manually adding them
to a zone, a time stamp of zero is set. This makes these records ineligible
for use in aging/scavenging operations.

In order to change this default, you can administer these records individually,
to reset and permit them to use a current (non-zero) time stamp value. This
enables these records to become aged and scavenged.

Note

In the case of changing a zone from standard primary to Active Directory-integrated,
you might want to enable scavenging of all existing resource records in
the zone. To enable aging for all existing resource records in a zone, you
can use the AgeAllRecords command, which is available through the
dnscmd command-line tool.